[Objectives]  To investigate the migration of Spodoptera frugipeda in southern Yunnan and identify the source of migrating insects. [Methods]  An automatic searchlight trap was used to systematically monitor the movements and population dynamics of S. frugipeda in southern Yunnan in 2020. We inferred the source population based on trapping data, and by integrating meteorological data with insect flight trajectory simulation. [Results]  S. frugipeda moths were caught all year round, and there were multiple monthly peaks of abundance from March to April and June to October. The population dynamics of S. frugipeda in this region is complex, with populations comprised of varying proportions of local and migrating individuals in different seasons. From January to February, most moths were of local origin and are unable to migrate northward due to low temperatures. From March to April, captures consisted of a mix of locally bred and immigrant moths, with emigrating moths that reach Guizhou and Guangxi primarily originating from southeastern Myanmar. From May to July, a higher proportion of moths were captured in the latter half of the night in Jiangcheng, indicating immigration from outside China, whereas in Yuanjiang, most moths were captured in the first half of the night, indicating continuous northward migration. From August to October, the proportion of moths captured throughout the night stabilized, indicating a mixture of local and immigrant moths. Most immigrants came from locations within China such as Guizhou and Sichuan. Local moths are capable of migrating to other countries such as Myanmar. [Conclusion]  These results provide sights into the population dynamics and migratory behavior of S. frugipeda in southern Yunnan, and also elucidate the immigration, emigration, and atmospheric factors that influence the migration of this species. These findings contribute to our understanding of S. frugipeda population dynamics in different seasons, thereby providing information to improve the monitoring of S. frugipeda, including providing early warning of outbreaks, not only in Yunnan, but also in other parts of China.